sealing holes

So in my home made AIO baffle system using a pvc baffle I have came across a problem. The outer seam on the return chamber has blown out, and so it is effectively bypassing the heater and filtration (I would say only about 10% of the flow through those chambers. So I temporarily moved the...

So I've removed one of the overflows in a 120 I recently got. The tank is going to be laid out like a peninsula so no need for these 2 holes now. Ive got to look around for a local glass shop and see what it will cost to get them to cut me a chunk of 3/8" glass to cover them. But I was also...